Method for improving an air circulation and a way for heating air in a glass tempering oven

ABSTRACT

Method for tempering glass in an oven ( 1 ) in which oven the glass (G) is moved while resting on rolls ( 4 ) in horizontal plane and of heating of the glass a significant part occurs with convection air which is circulated with the help of one or several blowing units (BU) which air is heated with heating resistors ( 5 ) which are located inside a blowing chamber ( 3 ) and are mainly located in longitudinal direction regarding the oven after which the air is blown towards the glass (G) through nozzle rows ( 6   n ). A roll space ( 8 ) and a suction space ( 7 ) are separated with the help of pressure from each other by extending the length of a plate ( 9 ) and width measures to be essentially larger than the length and/or the width of the blowing chamber ( 3 ) or by arranging an element ( 7   co ), ( 7   cov ), ( 9   e ) of other kind which constricts the flow of the air between the roll space ( 8 ) and the suction space ( 7 ) thanks to which elements the underpressure of the suction space ( 7 ) has an effect totally or at least for the most part on suction channels ( 7   c ), ( 7   ce ) or has an effect on a suction space ( 7   i ) and only a little bit on the roll space ( 8 ) in which case the convection air is sucked at least mainly from the roll space through the mentioned suction channels and the suction space.

Object of the invention is a method for tempering glass in an oven in which oven the glass is moved while resting on rolls in horizontal plane and during the heating of the glass a significant part of heating occurs with convection air which is circulated with the help of one or several blowing units which air is heated with heating resistors which are located inside a blowing chamber and are mainly longitudinal regarding the oven after which the air is blown towards the glass through nozzle rows.

Known Technology:

A Finnish patent FI-111006 and a U.S. Pat. No. 7,290,405, FIGS. 10 and 11 show a convection arrangement which in practise has proven to be very efficient and well functioning. In the arrangement the pipes of the resistors must be taken through each air channel (nozzle section). The sealing between pipes and channels must be made well. There is a large number of points to be sealed. Making of perforations and sealings causes unnecessary costs and loss related to escape of convection air. The requirement of an efficient convection is the fact that convection air showers meet the glass with great speed. Arrangements according to the FIGS. 7, 8, and 9 of the patent FI-111006 have also been realized but have been found to be much weaker. The reason is the fact that return air cycle interferes with convection air showers and reduces the incidence speed of the air showers coming from the nozzles to the glass. FIG. A clarifies the disadvantage of the return flow for convection showers. The capacities of these kind of convection arrangements are approximately 20-40% lower than the methods according to the FIGS. 10 and 11 of the patent FI-111006 depending on the glass type. In addition to that convection air showers should have a heating profile required by each load of glass. Air flowing to the sides also weakens hugely the heating profile. The method according to the patent FI-111006 has thus been found to be the best and the most inexpensive convection arrangement in which method convection air shower areas and exit air areas alternate in relation to the direction of motion of the glass on transversal sectors. The methods according to the FIGS. 1-6 of the patent FI-111006 cannot be realized so that they would be technically correct regarding the air flow and reasonable regarding their costs.

One section which has disadvantages in the patents FI 111006 and FI 20030482 and for example in the patent application 2013 0238 relates to the changing of the heating resistors. It must be performed at the end of the oven because the resistors are long and they are inside casings or pipes. The other disadvantage of the resistors is the fact that the adjusting of the temperature of the oven occuring in a longitudinal direction is difficult, an example is the transverse resistors of the oven described in the patents FI 111006 and FI 20030482. The third disadvantage is the fact that the mentioned ovens FI 20030482 have long nozzle casings and the oven FI 111006 has long pipes for the resistors. The control of their thermal expansion is difficult in relation to other structures, especially in relation to blowing units located in stationary points. Sealings in the thermal expansion points are difficult to realize and escape of the convection air causes loss of power and energy loss.

Efficiency of the convection can be increased, the temperature profile can be improved, the loss of convection air can be reduced and costs can be cut when one acts in the innovative way described in the following:

FIGURES AND THEIR EXPLANATIONS

FIG. A shows a disadvantageous return air flow which is directed sidewards which return air flow interferes with the efficiency of the convection air showers. This disadvantage can advantageously be removed in the way which is described in this application.

FIG. B shows an efficient convection according to the patent FI-111006 during which blowing units (BU) are arranged inside the tempering oven one after another above the rolls 4. The heating resistors 5 are most advantageously installed inside the pipes which pipes penetrate the walls of the nozzle casings which are located to be an extension to the blowing chamber 3.

FIG. 1A shows a cross section of the oven 1 in which oven the blowers 2 are located at both sides of the blowing chamber 3. The air from the blowers is directed from between the resistors 5 to the nozzles 6 n which are penetrated into the wall 9, the convection showers 6 are directed to the glass G which moves on the rolls 4.

FIG. 1B corresponds to the FIG. 1A with the difference that the blowers which blow in two directions are located in the middle of the oven, such as is shown also in the FIG. B. The blowing chamber(s) are now located at both sides of the blowers but they are combined underneath the blowers. Also the space underneath the blowers now belongs to the suction chamber. Depending on the output of the blower 2 they can be arranged to blow also into two consecutive blowing units regarding the direction of the oven in order to cut the costs.

The section A-A of the FIGS. 1A and 1B shows how air is returned from the roll space 8 to the channel 7 c shown as a section and along the channel through a gap 7 d into the suction chamber 7. The suction chamber comprises the whole upper part of the roll space 8 excluding the blowing chamber 3 and the blowers 2.

FIG. 2 is a side view of the oven arrangement which arrangement comprises blowing units BU one after another and a gap G1 is left between them. The majority, even almost all return air can be returned by utilizing the gap G1 into the suction chamber 7 in which case the width of the oven can be made smaller by reducing the measure 7 d and the pressure loss of the return air flow can be reduced. Part of the air can further be returned along the channels 7 c and along the space 7 d. The parts 3 e in the drawing illustrate intermediate spaces which combine the blowing chambers 3 to each other. Their purpose is to balance air flow between the blowing chambers 3 and enable the usage of the machine even though one of the warm-air heaters 2 might be broken. FIG. 2 also shows the essential feature of the invention, return air flows must be constricted above the roll space 8 and underneath the actual return air channels 7 co and 7 cov so that the desired, controlled air flow can be created.

FIG. 2A shows an embodiment of the invention with the help of which a greater part or even nearly all return air can be returned through the gap G1. So that the flow in the direction of the oven in the roll space 8) would not increase so that it would interfere with the convection air showers, it is possible to add channels 7 ce above the channels 7 c which channels are transverse in relation to them and longitudinal in relation to the oven. Through these channels a majority of the convection air produced by each blowing unit BU can be sucked into the suction chamber 7 through the gap G1. The section A-A in the figure illustrates return channels 7 c and 7 ce at the location of the channel 7 c. The section B-B is a section between the channels 7 c. The nozzle casing extends from one edge of the oven to the other in which case the convection air showers cover evenly the width of the whole oven.

FIG. 3 shows an alternative return circulation of the air during which air channels which are like the channels 7 c, 7 ce are not used but the return air is circulated into the suction chamber and back to the blowers in the space 7 i which is between the lower wall of the blowing chamber 3 and the spacer plate either in a longitudinal direction regarding the oven to the space G1 or in a lateral direction to a space 7 d or in both directions. There are gaps in the spacer plate 9 for tubular nozzles or tubular nozzles 6 n are attached to them through which nozzles convection air showers are directed to the glass G. Gaps 7 co are pierced into the spacer plate 9 and gaps or holes 7 cov are left which create the needed restriction which is needed to create the pressure difference between the roll space 8 and the suction chamber 7. The return air flows to the space 7 i between the plate 9 and the lower wall of the blowing chamber 3 and further to the suction chamber 7. For example largish gaps which are made for the tubular nozzles, separate holes or elongated holes can be used as gaps depending on how the nozzle rows are arranged and how underpressure distribution which is advantageous for the return air flows can be created. When the length of the tubular nozzles is adjusted to be such that they extend to the level of the spacer plate 9, the return air flow moving in the intermediate space 7 does not interfere with the convection air showers. FIGS. 4A(1), 4A(2) and 4A(3).

Details are shown of the part between the wall of the oven and the blowing unit at the location of the return air channel 7 c and/or details of the method according to the way shown in the FIG. 3. It shows how the roll space 8 must be separated at least mostly at the location of the hole 7 d leading to the suction chamber 7 so that at most only minor underpressure is directed directly to the roll space 8, but underpressure and air flow are directed in a controlled way through the channel 7 c or 7 ce or 7 cev or through the space 71. Parts 9 e illustrate alternative restriction ways. One restriction way may also be the sizing and design of the blowing chamber in such a way that the right kind of restriction can be created.

FIG. 4B shows the reciprocal location and the advantageous structure of two blowing units BU and their blowing chambers 3 as a side view of the oven in which figure the nozzle casing part 3 nb of the blowing chamber is broadened at its lower part and correspondingly the suction channel 7 c is broadened at its upper part. Thus the desired restriction and pressure difference between the roll space 8 and the suction channels 7 c and the suction chamber 3 can be created. In addition to that the nozzles can be spread to a wider surface area in which case the heat transfer becomes more effective.

FIG. 5 shows the oven structure which is described earlier but for clarity reasons the mentioned descriptions of the inventive parts of the air flows are mainly left out. The figure shows how the resistors 5 have now been built to have approximately the length of the blowing chamber 3 and how the blowing chamber is divided above the resistors 5 into two parts along the line 3 s. The lower part 3 b of the blowing chamber can be detached and lowered down either fully or can be equipped with hinges at its other edge. The resistors 5 which are located at the lower part of the blowing chamber 3 are most advantageously installed to the pipes. The resistors or the pipes are attached at least nearly air-sealed to the walls of the blowing chamber at their ends or near their ends.

Underneath the glass an efficient convection heating is not needed because there is no coating underneath the glass. However, it is important to keep the temperature of the rolls 4 stable. Radiation is not good enough for this. That is why the heat transfer must be boosted with the help of the convection. Additionally, because the upper and lower heat regulation must be “synchronized”, the upper and lower resistors must be located on top of each other in relation to each other. In order to perform the necessary heat transfer advantageously and in the right way, the best way to perform it is to install the resistors underneath the glass which resistors correspond to the length and location of the upper resistors. Most advantageously the needed addition of the heat transfer can be realized with convection and nozzle casings 3 db from between the lower resistors from which resistors air showers are directed to the rolls 4 in different angles being measured from the horizontal plane so that the convection is directed to all rolls.

FIG. 6 shows how the upper part of the oven is lifted to an upper position when the resistors are being changed. Then the part 3 b can be lowered downwards in which case the changing of the resistors can be done easily. FIG. 6 shows the hinge alternative in order to lower the lower part 3 b of the blowing chamber 3 into the lower position so that the resistors 5 can be pulled out and pushed in without the adjacent blowing unit BU interfering because there is no need to change the resistors. There is no need to present the cables of the resistors, connections, thermocouples and mechanisms of the lifting process because several known alternatives exist for them. The lifting device 9 can also be located on the top of the oven, if wanted. If one wants to lower down the lower part 3 b in horizontal plane, the lifting devices are needed at both ends of the blowing chamber. Organizing the needed additional length for the cablings, which is needed for lowering down the resistors, can be organized on top of the oven, if wanted, in which case a down/up movement possibility is arranged for them to that location.

FIG. 7. A sealing arrangement between the resistor pipes 5 and the wall of the blowing chamber 3 in which arrangement holes Dh, which are considerably larger than the outer diameter Dp of the pipe, are machined to the wall of the pressure chamber and to the holder Sh of the seal while the hole of the seal part S is only a little bit larger than the hole of the outer diameter of the pipe. When the outer diameter Do2 of the holder of the seal is considerably larger than the outer diameter Do1 of the seal and the hole, which is left for the seal, is only a little bit larger than the thickness of the seal, a good enough sealing can be achieved for the convection air while the resistance tube 5 can move in longitudinal direction and at the same time the resistance tube can also move radially in every direction.

By realizing the insulation of the upper convection from the roll space 8 according to the FIG. 4 with the arrangement in question the heating resistors 5 can be located immediately on top of the return air channels 7 c, 7 ce or on top of the return air space 7 i, most advantageously inside the pipes in which case numerous perforations can be avoided according to the FIGS. 10 and 11 from the patent FI-111006. With the help of this method manufacturing costs, difficulties caused by thermal expansions and sealing problems can be considerably decreased.

The mentioned disadvantages on the page 1 on the lines 27-34 can be removed and one can achieve a) heat regulation also in the longitudinal direction regarding the oven in which case a “matrix” heat regulation can be created with the transverse profile of the heat, b) easily performed changing of the resistors and c) controlling of the thermal expansions and at the same time a nearly complete removal of escape air when one acts in the inventive way described in the following. 

1. Method for tempering glass in an oven (1) in which oven the glass (G) is moved while resting on rolls (4) in horizontal plane and of heating of the glass a significant part occurs with convection air which is circulated with the help of one or several blowing units (BU) which air is heated with heating resistors (5) which are located inside a blowing chamber (3) and are mainly located in longitudinal direction regarding the oven after which the air is blown towards the glass (G) through nozzle rows (6 n), characterized in that a roll space (8) and a suction space (7) are separated with the help of pressure from each other by extending the length of a plate (9) and width measures to be essentially larger than the length and/or the width of the blowing chamber (3) or by arranging an element (7 co), (7 cov), (9 e) of other kind which constricts the flow of the air between the roll space (8) and the suction space (7) thanks to which elements the underpressure of the suction space (7) has an effect totally or at least for the most part on suction channels (7 c), (7 ce) or has an effect on a suction space (7 i) and only a little bit on the roll space (8) in which case the convection air is sucked at least mainly from the roll space through the mentioned suction channels and the suction space.
 2. Method according to the claim 1, characterized in that the return air from the roll space (8) to the suction space (7) and back to the blowers (2) is mainly directed in the channels (7 c), (7 ce) arranged between the resistors (5) and the exhaust passages of the nozzles (6 n) or is directed in the spaces (7 i).
 3. Method according to the claim 1, characterized in that with the help of the design and/or the sizing of the blowing chamber (3) one can create the restriction and pressure difference between the suction space (7) and the roll space (8).
 4. Method according to the claim 1, characterized in that a spacer plate (9), which has at least nearly the same direction as the lower surface of the blowing chamber, is arranged underneath the blowing chambers (3) which spacer plate forms a intermediate space (7 i) through which convection air showers are brought to the roll space (8) with (the help of) elongated nozzles (6 n) and return air gaps are arranged to the plate (9) through which at least the majority of the return air is sucked into the intermediate space (7 i) and further through the spaces (G1) and/or (7 d) into the suction chambers (7).
 5. Method according to the claim 1, characterized in that intermediate spaces (G1) are arranged between the blowing chambers (3) with the help of which intermediate spaces the suction chambers (7) of the blowing units (BU) are combined.
 6. Method according to the claim 1, characterized in that the blowing chamber (3) is divided into two parts of which parts the lower part (3 b) can be detached, lowered down or is hinged in such a way that it is possible to change the resistors (5).
 7. Method according to the claim 1, characterized in that the lower resistors (5 b) of the oven are divided into parts in longitudinal direction regarding the oven in which case the blowing of the convection air is performed from a nozzle casing (3 db) which is located in a space between the ends of the resistors.
 8. Method according to the claim 1, characterized in that the sealing between the heating resistor pipe (5) and the wall of the blowing chamber (3) is realized with a seal (S) which is closed in a hole space between the wall of the blowing chamber (3) and the holder (Sh) of the seal the width (1) of which space is adjusted to be only a little bit larger than the thickness of the seal (S) and the seal (S) is adjusted to have a form of a disc the inner hole of which disc is only a little bit larger than the outer diameter of the thermal resistance (5) and the outer diameter Do1 of which disc is smaller than the outer diameter (Do2) of the holder (Sh) of the seal. 